The field of the invention is systems and methods for x-ray imaging, including x-ray computed tomography (“CT”). More particularly, the invention relates to systems and methods for photon-counting detector computed tomography (“PCCT”).
PCCT systems have the potential to greatly increase the medical benefits of CT. Unlike “traditional” CT detectors, which integrate the charge generated by x-ray photon interactions in the detector but provide no specific energy information regarding individual photons, photon-counting detectors record the energy deposited by each individual photon interacting with the detector. PCCT systems can thus be used to differentiate materials, such as a contrast agent in the blood and calcifications that may otherwise be indistinguishable in traditional CT systems.
PCCT systems can also be used to improve the signal-to-noise ratio (“SNR”) by reducing electronic noise. In general, PCCT systems produce less image noise for the same patient dose than traditional CT systems and, hence, can be more dose efficient than these conventional CT systems. Also, PCCT systems can improve SNR by assigning optimal, energy dependent weighting factors to the detected photons and can achieve additional SNR improvements by completely or partially rejecting scattered photons. Further still, use of a PCCT system allows measurement of transmitted, energy-resolved spectra from a single exposure at one tube potential.
PCCT systems can perform multi-energy measurements for N≥2 energy levels. In some configurations, measurements are obtained on the same pixel with N identical energy thresholds on the same detector element. Images with higher energy resolution can then be generated based on a subtraction between measurements from the same pixel. In some other configurations, cross-pixel measurements are obtained with different energy thresholds on the same detector element. Images with higher energy resolution are then generated based on a subtraction between measurements from different pixels.
Selection of the x-ray tube spectra, energy thresholds, and energy bins that are used in PCCT has a significant effect on the resulting image quality, material decomposition capability, and radiation dose imparted to patients. Because the degree of freedom for optimizing the selection of the x-ray tube spectra, energy thresholds, and energy bins is very high, it would be desirable to have a systematic optimization scheme for selecting these parameters before initiating a patient scan.